This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-031529 filed in Japan on Feb. 16, 2010, the entire contents of which are herein incorporated by reference.
The present invention relates to an illuminating device for illuminating an irradiation target such as a document, an image-reading apparatus provided with the illuminating device, and an image-forming apparatus provided with the image-reading apparatus.
This type of illuminating device is used mounted on, for example, an image-reading apparatus, is provided with a plurality of light-emitting elements (e.g., LEDs) that are arranged in a line parallel to a main-scanning direction for reading a document, and illuminates a document using these light-emitting elements. The image-reading apparatus repeatedly scans a document illuminated by the illuminating device in the main-scanning direction, and, at the same time, scans the document also in a sub-scanning direction, thereby reading the entire document. An image of this read document is output to a printer or the like, and recorded on recording paper.
In such an illuminating device, as the number of the light-emitting elements increases, a higher illuminance can be achieved. However, because of a high unit cost of the light-emitting element, it is desirable to reduce the number of the light-emitting elements to reduce the cost and also the power consumption.
Also, the light-emitting elements have a narrow directivity, the light intensity of the light-emitting elements in the optical axis direction is strong, and the light intensity decreases as the light deviates from the optical axis, and thus uneven illumination in which the bright spot of the light-emitting elements is reflected in a document reading range readily occurs, and it is desirable to reduce uneven illumination.
In order to solve such problems, JP 2005-102112A (Patent Document 1) discloses a technique in which a condensing element is provided in the light-emitting direction of the respective light-emitting elements, such that almost all of the light emitted from the light-emitting elements is caused to be incident on the incident-side lens of the condensing element and are emitted from the condensing element onto a document reading range, or such that, by forming a prismatic surface in a part of the condensing element or providing a reflecting plate as a separate element from the condensing element, light that has been transmitted through the condensing element is reflected by the prismatic surface or the reflecting plate so as to allow the light to be emitted toward the document reading range, thereby reducing the light loss. Such reduction of the light loss enables reduction of the number of light-emitting elements.
Also in JP 2001-343531A (Patent Document 2), in a configuration in which light of the light-emitting elements is emitted onto an irradiation target via a light guide plate, the light emitting face of the light guide plate is given a light diffusing function to diffuse light by the light emitting face of the light guide plate, thereby reducing uneven illumination on the irradiation target. With such a configuration, even though the number of light-emitting elements is small, uneven illumination hardly occurs.
However, in the technique of Patent Document 1, although the light loss can be reduced, no particular measure to reduce uneven illumination is disclosed.
Also in Patent Document 2, while uneven illumination on the irradiation target is reduced by diffusing light by the light emitting face of the light guide plate, the light loss increases due to such diffusion of light, which results in a significant decrease in the irradiation light amount onto the irradiation target.
The present invention was arrived at in view of the above-described conventional problem, and it is an object thereof to provide an illuminating device capable of effectively reducing the light loss while suppressing uneven illumination by a plurality of light-emitting elements, an image-reading apparatus including such an illuminating device, and an image-forming apparatus including such an image-reading apparatus.